Biosolids Management Program

King County uses biosolids to improve soils and enhance plant growth. The Biosolids Management Program is responsible for activities associated with recycling biosolids: transportation, land application, research, public information, monitoring, state permits, market development and planning.

Biosolids are recycled as a fertilizer and soil conditioner in agriculture and forestry, and in a variety of research and environmental restoration projects. A portion of our biosolids is composted by a private company for use in landscaping and gardening. Biosolids from King County have been recycled since 1973.

Biosolids Quality

Biosolids contain nitrogen, phosphorus, potassium, sulfur and other nutrients needed by plants. To ensure the quality and safety of biosolids, the physical, chemical and microbial characteristics are regularly monitored.

Since the early 1980's, King County's industrial waste source control and pretreatment program has significantly reduced the amount of trace metals and other pollutants entering the treatment system. Biosolids quality has greatly improved due to source control efforts combined with City of Seattle's efforts to reduce metals from corrosion of water pipes, and the gradual elimination of leaded gasoline. The Local Hazardous Waste Management Program provides education, collection and technical assistance to small businesses and citizens on proper handling of materials which could pose a threat to wastewater and biosolids quality.

King County biosolids treatment processes reduce the pathogens typically found in wastewater by about 95%. These biosolids meet Class B pathogen reduction criteria and are safe for a variety of beneficial uses. We continue to evaluate alternative treatment technologies which may reduce pathogens to meet Class A criteria in addition to providing other benefits.

Regulatory Standards

King County biosolids meet the quality standards set by the U.S. Environmental Protection Agency (EPA; 40 CFR 503), which were adopted in 1998 by the Washington State Department of Ecology (WAC 173-308). The EPA technical standards were the result of many years of field research, detailed human health risk assessment, and careful review by a national panel of scientists with biosolids expertise.

Biosolids meeting Class B designation must be used according to certain site management restrictions. In order to be used in areas frequented by the public or on lawns or home gardens, biosolids must be treated further to virtually eliminate pathogens and meet the Class A pathogen reduction criteria. Biosolids may be composted to meet the Class A pathogen designation.

Research, Demonstration and Monitoring

A collaborative approach to research with Northwest Biosolids Management Association, University of Washington, Washington State University, Oregon State University, University of Idaho and University of British Columbia has led to consistent regional information for biosolids managers and enhanced our ability to create cost effective land application programs. An active research and demonstration program has improved both public awareness and acceptance of biosolids recycling. More on Research and Demonstration.